1. Field of the Invention
This invention relates to a reinforcing laminate for tire and a heavy duty pneumatic radial tire using the same. More particularly this invention relates to an improvement in the durability of carcass ply and belt layer using high elasticity cords in the radial tire for an airplane running at high speed under high internal pressure and high loading.
2. Related Art Statement
The conventional heavy duty pneumatic radial tire illustrated in FIGS. 6-7, for example, an airplane radial tire 1 comprises a carcass 5 of plural carcass plies each containing organic fiber cords 4 sustantially arranged in parallel to each other in the axial direction of the tire and covered with a coating rubber 3 as a part of a side portion 2. A belt of plural belt layers superimposed about a crown portion of the carcass 5 (not shown) and containing cords is arranged circumferentially of the tire or at a small angle with respect to the circumferential direction of the tire. The cord 4 in the carcass 5 is generally a nylon cord. Recently, an organic fiber cord having a high modulus of elasticity such as Kevlar cord (trade name) or the like is used as the cord 4. As shown in FIG. 7, the cords 4 in the two carcass plies of the carcass 5 are used so as to pile one upon the other at the same pitch P. When such an airplane radial tire is run at a high speed under a high internal pressure and a high loading, the deflecting deformation of the tire during the rotation under loading is large and corresponds to about 25%.about.40% of a sectional height of the tire. As a result, the deformation of the side portion 2 in the tire becomes large and particularly the bending deformation thereof is very large, resulting in the occurrence of a large repetitive compression strain F inside the carcass 5.
As shown in FIG. 8, the belt 15 is composed of a four layer lamination structure consisting of a first belt layer 15a to a fourth belt layer 15d. In the formation of the belt 15, a single cord 18 covered with a coating rubber 17 is first helically wound from an end of the first belt layer 15a and arranged in parallel to each other in the circumferential direction.
Then, the second belt layer 15b is piled on the first belt layer 15a, wherein the initial end of the rubber coated cord of the second belt layer 15b is placed just on the second wound rubber coated cord of the first belt layer 15a viewed from the initial end thereof. In this way, the first belt layer 15a to fourth belt layer 15d are successively piled one upon the other to form the belt 15.
As a result, the cords 18 in the belt are in an up and down laminated state between the adjoining belt layers (in the radial direction of the tire).
For instance, when the cord 4 in the carcass 5 as shown in FIG. 6 is a high elasticity cord having a less elongation such as steel cord or Kevlar cord, the side portion 2 of the radial tire 1 is largely deformed to cause the bending deformation of the carcass 5. Particularly, the cords 4 of the inner carcass ply 5A in the carcass 5 are subjected to a large repetitive compression strain F, whereby the fatigue of the cord 4 is accelerated to decrease the strength of the cord 4. Consequently there is a problem that the fatigue life of the cord largely reduces. Furthermore, as shown in FIG. 7, the distance R.sub.0 between the outer carcass ply 5B and the inner carcass ply 5A in the carcass 5 reduces to a distance R.sub.1 and consequently a large shearing strain is caused in a boundary 5a between the carcass plies and in a space 4a between the cords of the carcass plies to promote the peeling between the cord 4 and the coating rubber 3 or the compression fatigue of the rubber 3, resulting in the considerable degradation of the fatigue life of the carcass.
In the belt, the cords of the adjoining belt layers are plied one upon the other in up and down directions and made from polyaramide fiber having a high modulus of elasticity or the like. When the tire is run under loading, the belt has no room for mitigating a shock from exterior and consequently there is a fear of weakening the belt to the external shock.
When this type of the heavy duty pneumatic radial tire is run at a high speed while being subjected to a large tire deformation, there have been made various studies with respect to the magnitude of bending deformation and compression strain of the cord in the carcass, the magnitude of shearing strain between carcass plies and between the cords, the fatigue life of the carcass, the rubber thickness of the carcass ply, the arrangement of cords in the carcass ply and the like. Consequently the following has been confirmed. That is, as the rubber thickness between the carcass plies increases and also the distance between cords in the carcass ply increases, the shearing strain between the cords and between the carcass plies reduces, but the tire weight and quantity of heat build-up undesirably increase. Particularly, when the high elasticity cord is used, the difference in tension between the inner carcass ply and the outer carcass ply increases and the fatigue of the inner carcass ply becomes larger. On the other hand, as the distance between cords in the carcass ply becomes large, the shearing strain between the cords becomes small, but the strength of the carcass ply lowers, resulting in the increase of the carcass ply number. This brings about the increase of the tire weight and amount of heat build-up to degrade the durability of the tire.